Dc brushless motor for electrical power steering and the production method thereof

ABSTRACT

The stator core of a motor comprises an annular back core, and a plurality of tees created separately from the back core and secured onto the inner periphery of the back core. A stator coil is wound on each of the tees by a distributed or concentrated winding method. The stator core and stator coil are formed by molding.

This application is a divisional of U.S. patent application Ser. No.11/136,423, filed May 25, 2005, the entire disclosure of which isincorporated herein by reference, which in turn claims priority under 35U.S.C. § 119 of prior Japanese application no. 2004-165345, filed Jun.3, 2004.

FIELD OF THE INVENTION

The present invention relates to a DC brushless motor for electricalpower steering and production method thereof.

BACKGROUND OF THE INVENTION

In the prior art DC brushless motor for electrical power steering, theneed for reducing the torque pulsation is known, as described in theJapanese Patent Laid-open No. 2001-275325 and Japanese Patent Laid-openNo. 2003-250254.

SUMMARY OF THE INVENTION

Efforts have been made to reduce the torque pulsation, withoutsatisfactory reduction of torque pulsation having been achieved so far.One of the problems to be solved in the DC brushless motor forelectrical power steering is how to achieve a further reduction intorque pulsation.

The DC brushless motor for electrical power steering is required toreduce torque pulsation and to generate a large torque as required. Forexample, when the vehicle is stopped or is slowly running close to thestopped state, if the steering wheel is turned, the aforementioned motoris required to provide a large torque due to the friction coefficientbetween the steering wheel and ground surface.

To be more specific, another problem of the DC brushless motor forelectrical power steering is to find out a way for meeting bothrequirements for reduction of torque pulsation and production of a largetorque, so that torque pulsation can be reduced and a large torque canbe produced, whenever required.

The embodiments described below solve various problems found in the DCbrushless motor for electrical power steering. These solutions will bedescribed each of the following embodiments:

The present invention provides a DC brushless motor for electrical powersteering capable of more effective reduction of torque pulsation.

The DC brushless motor for electrical power steering is most typicallycharacterized in that a stator core is formed by connecting split corepieces, and the stator core and the stator coil built in this statorcore are molded by a molding agent, with the stator coil built in thisstator core.

The present invention provides a further reduction in torque pulsation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a transverse cross sectional view representing theconfiguration of the DC brushless motor for electrical power steering asan embodiment of the present invention;

FIG. 2 is a cross sectional view taken along line A-A of FIG. 1;

FIG. 3 is an explanatory diagram representing the relationship betweenthe numbers of poles P and slots S in an AC motor;

FIG. 4 is an explanatory diagram representing the actual measurements ofthe cogging torque in the DC brushless motor for electrical powersteering of an embodiment in the present invention;

FIG. 5 is a connection diagram of stator coils in the DC brushless motorfor electrical power steering according to the present embodiment of anembodiment in the present invention;

FIG. 6 is a side view representing the electrical connection of thestator coils in the DC brushless motor for electrical power steeringaccording to an embodiment in the present invention;

FIG. 7 is a view in the direction of the arrow A-A in FIG. 1, showingthe configuration of another stator;

FIG. 8 is a system configuration diagram representing the configurationof a steering system using the DC brushless motor for electrical powersteering according to an embodiment in the present invention;

FIG. 9 is a function block diagram representing the configuration of thecontroller for controlling the DC brushless motor for electrical powersteering of an embodiment in the present invention;

FIG. 10 is a perspective exploded view representing the configuration ofthe controller of the DC brushless motor for electrical power steeringof an embodiment in the present invention;

FIG. 11 is a circuit diagram representing the circuit configuration ofthe controller for controlling the DC brushless motor for electricalpower steering of an embodiment in the present invention;

FIG. 12 is a perspective bottom view showing the configuration ofconductor module of the controller for controlling the DC brushlessmotor for electrical power steering of an embodiment in the presentinvention;

FIG. 13 is a perspective view representing the configuration of thecontroller for controlling the DC brushless motor for electrical powersteering of an embodiment in the present invention;

FIG. 14 is a cross sectional view of the controller for controlling theDC brushless motor for electrical power steering of an embodiment in thepresent invention;

FIG. 15 is a cross sectional view representing the major portions of thecontroller for controlling the DC brushless motor for electrical powersteering of an embodiment in the present invention;

FIG. 16 is a cross sectional view representing the major portions of thecontroller for controlling the DC brushless motor for electrical powersteering of an embodiment in the present invention; and

FIG. 17 is a perspective view representing another configuration of thecontroller for controlling the DC brushless motor for electrical powersteering of an embodiment in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The DC brushless motor for electrical power steering of the presentinvention is most typically characterized as follows:

The present invention provides a DC brushless motor for electrical powersteering, driven by polyphase alternating current power, for outputtingsteering torque, the aforementioned DC brushless motor for electricalpower steering comprising a frame, a stator secured on theaforementioned frame and a rotor arranged opposite to the aforementionedstator through an air gap. This stator comprises a stator core and apolyphase stator coil built in the aforementioned stator core. Thestator core, formed by connecting a plurality of split core pieces,comprises an annular back core, and a plurality of tee cores projectedradially from the aforementioned back core. A slot is formed on theaforementioned tee core adjacent to the aforementioned stator core, andthe aforementioned stator coil is incorporated in the aforementionedslot. The rotor comprises a rotor core, and a plurality of magnets fixedonto the surface of the outer periphery of the rotor core. The statorcore and stator coil being molded by a molding agent, with the statorcoil incorporated in the stator core.

The method for manufacturing a DC brushless motor for electrical powersteering of the present invention is most typically characterized asfollows:

The present invention provides a DC brushless motor for electrical powersteering manufacturing method, driven by polyphase alternating currentpower, for outputting steering torque. This manufacturing methodcomprises a first step of assembling a stator coil into a stator core; asubsequent second step of press-fitting into the frame a plurality ofpositions of the stator core incorporating the stator coil in thecircumferential direction, and obtaining a structure composed of thestator core incorporating the stator coil, secured to the frame; asubsequent third step of mounting a jig on the aforementioned structurein such a way that the jig and frame will enclose the stator core andthe coil end of the stator coil protruding axially from the axial end ofthe stator core; a subsequent fourth step of injecting the molding agentinto the space enclosed by the jig and frame, thereby filling themolding agent into the air gap between the coil end and stator core, theair gap of the stator coil, the air gap between stator core and statorcoil, and the air gap between the stator core and frame; a subsequentfifth step of solidifying the molding agent; and a subsequent sixth stepof removing the jig.

Referring to FIGS. 1 through 9, the following describes theconfiguration and operation of the DC brushless motor for electricalpower steering as an embodiment of the present invention.

In the first place, the following describes the configuration andoperation of the DC brushless motor for electrical power steering of thepresent embodiment with reference to FIGS. 1 and 2:

FIG. 1 is a transverse cross sectional view representing theconfiguration of the DC brushless motor for electrical power steering ofthe present embodiment of the present invention. FIG. 2 is a crosssectional view taken along line A-A of FIG. 1. FIG. 2(A) is an overallcross sectional view and FIG. 2(B) is a cross sectional viewrepresenting the major portions.

The DC brushless motor for electrical power steering (hereinafterreferred to as “EPS motor”) 100 is a surface magnet type synchronousmotor comprising a stator 110 and the rotor 130 rotatably supportedinside this stator 110. The EPS motor 100 is driven by an on-board powersource equipped with a battery namely, by power supplied from a 14-voltpower source (12-volt battery output voltage), a 24-volt power source a42-volt power source (36-volt battery output voltage), or a 48-voltpower source, for example.

The stator 110 comprises a stator core 112 formed of a magneticsubstance laminated with a silicon steel plate and a stator coil 114held inside the slot of the stator core 112. The stator core 112 iscomposed of an annular back core and a plurality of tees createdseparately from this back core and mechanically fixed onto the back corethereafter, as will be described later with reference to FIG. 2. Each ofthe tees is wound with a stator coil 114. The stator coil 114 is woundby a distributed or concentrated winding method.

The stator coil 114 wound according to the distributed winding method ischaracterized by excellent field weakening control and occurrence ofreluctance torque. Downsizing of the motor and reduction of windingresistance are very important for the EPS motor. The length of the coilend of the stator coil 114 can be reduced by concentrated winding of thestator coil 114. This arrangement reduces the length of the EPS motor100 in the direction of rotary axis. Further, since the length of thecoil end of the stator coil 114 can be reduced, the resistance of thestator coil 114 can be reduced, and rise in motor temperature can alsobe reduced. Reduction in coil resistance minimizes the motor copperloss. Thus, the percentage of the energy consumed by copper lossrelative to the entire energy inputted into the motor can be reduced andthe efficiency of the output torque relative to input energy can beimproved.

As described above, the EPS motor is driven by the power source mountedon a vehicle. The output voltage of the aforementioned power source isoften low. A series circuit is equivalently formed by the switchingdevice with an inverter formed across the power source terminal, theaforementioned motor and other current supply circuit connecting means.In the aforementioned circuit, a total of the terminal voltage of thecircuit constituent devices becomes the terminal voltage of theaforementioned power source. Thus, the terminal voltage of the motor forsupplying power to the motor is lowered. To ensure the current flowinginto the motor under this condition, it is crucial to keep the copperloss of the motor low. For this reason, a low-voltage system of 50 voltsor less is often used as the power source mounted on a vehicle. Theconcentrated winding method is preferably applied to the stator coil114. This is very important especially when a 12-volt power source isused.

The power steering motor is placed close to the steering column or closeto a rack-and-pinion mechanism. Downsizing is required in either case.In the downsized structure, the stator winding must be fixed inposition. It is also important to make winding work easy. Concentratedwinding ensures easier winding work and fixing work than distributedwinding.

The end of the stator coil 114 is molded. The EPS motor preferably keepsthe torque fluctuation such as cogging torque to a very low level. Afterthe stator section has been assembled, machining may be performed againinside the stator. Chips will be produced by such machining operation.Means must be provided to prevent these chips from entering the end ofthe stator coil. The coil end is preferably molded. The coil end refersto the position protruding in the axial direction from both axial endsof the stator core 112. In the present embodiment, an air gap isprovided between the mold resin covering the end of the stator coil 114and a frame 150. The molding agent can be filled up to the positioncoming in contact with the frame 150, a front flange 152F and a rearflange 152R. This arrangement ensures that heat generated from thestator coil 114 is transferred from the coil end through the mold resindirectly to the frame 150, front flange 152F and rear flange 152R, andis released to the outside. As compared with heat transmission throughair, this method reduces temperature rise of the stator coil 114effectively.

The stator coil 114 is composed of three phases; U, V and W phases. Eachcoil is made up of a plurality of unit coils. These unit coils areconnected for each phase by a connection ring 116 arranged on the leftof the drawing, as will be described with reference to FIG. 3.

The EPS motor is required to provide a large torque. For example, whenthe vehicle is stopped or is running close to the stopped state, if thesteering wheel is turned at a high speed, the aforementioned motor isrequired to provide a large torque due to the friction coefficientbetween the steering wheel and ground surface. In this case, a largecurrent is supplied to the stator coil. This current can be 50 amperesor more, although it depends on conditions. Further, it can be 70 or 150amperes. To ensure safe supply of such a large current and reducegeneration of heat by the aforementioned current, it is important to usethe connection ring 116. Current is supplied to the stator coil throughthe connection ring 116, whereby the connection resistance is loweredand voltage drop resulting from copper loss is minimized. Thisarrangement provides easy supply of a large current and reduces the timeconstant for current startup caused by the operation of the inverterdevice.

The stator core 112 and stator coil 114 are molded by resin(electrically insulating type) together to form an integral piece, andconstitutes a stator subassembly. This integral stator subassembly ispress-fitted into the cylindrical yoke 150 formed of metal such asaluminum and is fixed therein; this integral stator subassembly ismolded under this condition. The integral stator subassembly can bemolded, with the stator coil 114 built in the stator core 112, and canbe press-fitted in position thereafter.

The EPS on board a vehicle is subjected to various forms of vibration,as well as the impact from the wheel. Further, it is used under thecondition of a drastic temperature change. It may be exposed to thetemperature of 40° Celsius below zero, or 100° C. or more due totemperature rise. Further, means must be taken to prevent water fromentering the motor. In order for the stator to be fixed to the yoke 150under these conditions, the stator subassembly is preferablypress-fitted into a cylindrical metal free of any hole such as a screwhole, on the outer periphery of at least the stator core of thecylindrical frame. After pressing fitting, screws may be used to fix itin position, from the outer periphery of the frame. In addition to pressfitting, locking is preferably provided.

The rotor 130 comprises a rotor core 132 formed of a magnetic substancelaminated with a silicon steel plate; magnets 134 as a plurality ofpermanent magnets bonded on the surface of the rotor core 132 byadhesive; and a magnet cover 136 composed of non-magnetic substanceprovided on the outer periphery of the magnets 134. The magnet 134 is arare-earth magnet and is composed of neodymium, for example. The rotorcore 132 is fixed on the shaft 138. A plurality of magnets 134 arebonded on the surface of the rotor core 132 by adhesive. At the sametime, the outer periphery is covered with a magnet cover 136, wherebythe magnet 134 is prevented from being thrown away. The aforementionedmagnet cover 136 is made stainless steel (commonly known as SUS). It canbe wound with tape. Use of the stainless steel provides easierproduction. As described above, the ESP motor is suited to hold thepermanent magnet that is subjected to severe vibration and thermalchange, and is easy to break down. Even if it breaks down, it isprevented from being thrown away, as described above.

A front flange 152F is arranged on one end of the cylindrical frame 150.The frame 150 and front flange 152F are fixed together by a bolt B1. Arear flange 152R is press-fit into the on the end of the frame 150. Abearing 154F and a bearing 154R are mounted on the front flange 152F andrear flange 152R, respectively. A shaft 138 and a stator 110 fixed onthis shaft 138 are rotatably supported by these bearings 154F and 154R.

The front flange 152F is provided with an annular protrusion (orextension). The protrusion of the front flange 152F is extended in theaxial direction from the coil end side of the front flange 152F. Whenthe front flange 152F is secured to the frame 150, the tip of theprotrusion of the front flange 152F is inserted into the air gap formedbetween the molding agent of the coil end on the side of the frontflange 152F and the frame 150. To encourage heat radiation, theprotrusion of the front flange 152F is preferably kept in close contactwith the molding agent of the coil end on the side of the front flange152F.

The rear flange 152R is provided with a cylindrical recess. The recessof the rear flange 152R is concentric with the center axis of the shaft138, and is located axially inwardly (on the side of the stator core112) from the axial end of the frame 150. The tip of the recess of therear flange 152R extends toward the inner diameter side of the coil endon the side of the rear flange 152R, and is located radially opposite tothe coil end on the side of the rear flange 152R. A bearing 154 is heldby the tip of the recess of the rear flange 152R. The axial end of theshaft 138 on the side of the rear flange 152R extends further inwardly(opposite to the rotor core 132 side) from the bearing 154 to reach theposition close to the opening of the recess of the rear flange 152R, orthe position protruding slightly outwardly from the opening in the axialdirection.

A resolver 156 is arranged in the air gap formed between the innerperipheral surface of the recess of the rear flange 152R and the outerperipheral surface of the shaft 138. The resolver 156 is provided with aresolver stator 156S and is located outwardly (opposite to the rotorcore 132 side) from the bearing 154R in the axial direction. Theresolver rotor 156R is secured on one end (left end in the drawing) ofthe shaft 138 by a nut N1. When the resolver holding plate 156B issecured on the rear flange 152R by a screw SC1, the resolver stator 156Sis secured on the inner periphery of the recess of the rear flange 152R,and is arranged in opposite position through the resolver rotor 156R andair gap. The resolver 156 is composed of the resolver stator 156S andresolver rotor 156R. The rotation of the resolver rotor 156R is detectedby the resolver stator 156S, whereby the positions of a plurality ofmagnets 134 can be detected. To put it more specifically, the resolvercomprises a resolver rotor 156R having a concavo-convex pattern on theouter peripheral surface (e.g. elliptical or petal-shaped), and aresolver stator 156S wound with two output coils (displaced 90°electrically) and exciting coil. When a.c. voltage is applied to theexciting coil, a.c. voltage conforming to the variation in the length ofthe air gap between the resolver rotor 156R and resolver stator 156Soccurs to two output coils, wherein this a.c. voltage has a phasedifference in proportion to rotary angle. Thus, the resolver is intendedto detect two output voltages having a phase difference. The magneticpole position of the rotor 130 is detected by finding out the phaseangle from the phase angle of the two output voltage having beendetected.

Power is supplied from an external battery to each of the U, V and Wphases through a power cable 162. The power cable 162 is mounted on theframe 150 by a grommet 164. The magnetic pole position signal detectedfrom the resolver stator 156S is taken out by the signal cable 166. Thesignal cable 166 is mounted on the rear holder 158 by the grommet 168.The connection ring 116 and part of the power cable 1 are moldedtogether with the coil end.

The following describes the configuration of the stator 110 and rotor130 more specifically with reference to FIG. 2. FIG. 2 is a view in thedirection of the arrow A-A in FIG. 1. FIG. 2(B) is an enlarged crosssectional view of the section P in FIG. 2(A). The same referencenumerals as those in FIG. 1 indicate the same parts.

The stator 110 will be described first. The stator core 112 shown inFIG. 1 is composed of an annular back core 112B and a plurality of tees112T provided separately from this annular back core 112B. The annularback core 112B is made of a lamination of magnetic sheet metals such assilicon steel plate stamped out by press molding.

The tee 112T is composed of twelve independent tees 112T (U1+), 112T(U1−), 112T (U2+), 112T (U2−), 112T (V1+), 112T (V1−), 112T (V2+), 112T(V2−), 112T (W1+), 112T (W1−), 112T (W2+), and 112T (W2−). The tees 112T(U1+), 112T (U1−), 112T (U2+), 112T (U2−), 112T (V1+), 112T (V1−), 112T(V2+), 112T (V2−), 112T (W1+), 112T (W1−), 112T (W2+), and 112T (W2−)are wound with stator coils 114 (U1+), 114 (U1−), 114 (U2+), 114 (U2−),114 (V1+), 114 (V1−), 114 (V2+), 114 (V2−), 114 (W1+), 114 (W1−), 114(W2+), and 114 (W2−), respectively in a concentrated winding mode.

Here the stator coil 114 (U1+) and the stator coil 114 (U1−) are woundin such a way that current flows in the opposite directions. The statorcoil 114 (U2+) and the stator coil 114 (U2−) are also wound in such away that current flows in the opposite directions. The stator coil 114(U1+) and the stator coil 114 (U2+) are wound in such a way that currentflows in the same directions. The stator coil 114 (U1−) and the statorcoil 114 (U2−) are also wound in such a way that current flows in thesame directions. The relation of the directions of current flow for thestator coil 114 (V1+), stator coil 114 (V1−), stator coil 114 (V2+) andstator coil 114 (V2−), and the relation of the directions of currentflow for the stator coil 114 (W1+), stator coil 114 (W1−), stator coil114 (W2+) and stator coil 114 (W2−)are also the same as those in thecase of U phases.

Twelve tees 112T and stator coils 114 are manufactured in the samemanner. The tee 112T (U1+) and stator coil 114 (U1+) will be taken as anexample to explain the assembling process. The stator coil 114 (U1+) isa molded coil formed in such a way as to wind the tees 112T (U1+). Thestator coil 114 (U1+) is a pre-molded coil so as to be wound on the tee112T (U1+). The stator coil 114 (U1+) as the molded coil is moldedtogether with a bobbin 112BO. An integrated piece consisting of thestator coil 114 (U1+) and bobbin 112BO is fitted into the tee 112T (U1+)from its rear. The tip end of the tee 112T (U1+), namely, the sidefacing the rotor 130 is expanded in the circumferential direction. Thebobbin 112BO and stator coil 114 (U1+) serve as stoppers in thisexpanded section, and are anchored therein. The convex portion 112BKformed on the inner periphery of the back core 112B and a concaveportion 112TT shaped for fitting are formed on the rear of the tee 112T(U1+). The concave portion 112TT of the tee 112T (U1+) wound with themolded stator coil 114 (U1+) is press-fitted into the convex portion112BK of the back core 112B so that the tee 112T (U1+) is fastened onthe back core 112B. The above description applies also to the process ofmounting the stator coil 114 (U1−) through 114 (W2−) on the other tees112T (U1+) through 112T (W2−), and the process of mounting the othertees 112T (U1−) through 112T (W2−) on the back core 112B.

Twelve tees 112T equipped with stator coils 114 are secured on the backcore 112B, and a plurality of positions on the outer periphery of theback core 112B are press-fitted with the inner periphery of the frame150. Under this condition, the stator core 112 and stator coil 114 areintegrally molded by thermosetting resin MR to form a statorsubassembly. In the present embodiment, the stator coil 114 built in thestator core 112 is press-fitted with the frame 150. Under thiscondition, the stator core 112 and stator coil 114 are integrallymolded. This procedure has been described so far. It is also possible tomake such arrangements that, with the stator coil 114 is built in thestator core 112, the stator core 112 and stator coil 114 are integrallymolded and the stator core 112 is press-fitted with the frame 150subsequently.

In the processing of molding with molding agent, the jig (notillustrated) is mounted on the structure composed of the stator core 112and frame 150 in such a way that the stator core 112 and the coil end ofthe stator coil 114 protruding axially from the axial end of the statorcore 112 will be enclosed by the jig (not illustrated) and frame 150.Liquid molding agent is poured into the space enclosed by the jig (notillustrated) and the frame 150, thereby filling the molding agent intothe air gap between the core end and stator core 112, the air gap of thestator coil 114, the air gap between stator core 114 and stator coil114, and the air gap between the stator core 112 and frame 150. Then themolding agent is solidified. After it has solidified, the jig (notillustrated) is removed.

The inner peripheral surfaces of the molded stator subassembly, namely,the tips of the tees 112T (U1−) . . . 112T (W2−) as the surfacesradially opposite to the rotor 130 are provided with machining. Thisarrangement reduces the variation of the air gap between the stator 110and rotor 130, and further improves the roundness in the inner diameterof the stator 110. Further, integral molding ensure effective release ofthe heat generated by electric conduction of the stator coil 114, ascompared to the case where integral molding is not adopted. Further, themolding process protects the stator coil and tee against vibration.

For example, when the air gap between the outer periphery of the rotorcore of the rotor 130 and the inner periphery of the tee of the stator110 is 3 mm (3000 μm), the roundness of the inner diameter of about ±30μm will occur due to the production error of the back core 112B and tee112T, and assembling error of the back core 112B and tee 112T at thetime of press fitting and assembling. The roundness is equivalent to 1%(=30 μm/3000 μm) of the air gap, and therefore a cogging torque isproduced by the roundness of inner diameter. However, after molding, theinner diameter is machined. This process reduces the cogging torqueresulting from the roundness of the inner diameter. Reduction of thecogging torque improves the steering comfort.

Concave portions 150T are arranged inside the frame 150. Concaveportions 112BO2 are arranged on the outer periphery of the back core112B so as to be engaged with the concave portions 150T. The details areshown in FIG. 2 (B). The concave portions 150T and concave portions112BO2 constitute an engagement section IP having a mutually differentcurvature rate for engagement with each other. They are continuouslyformed in the axial direction. Eight of these portions are arranged at apredetermined interval in the circumferential direction. The engagementsection also serves as a press-fit section. To be more specific, whenthe stator core 112 is secured on the frame 150, the concave portions112BO2 of the back core 112B are press-fitted into the concave portions150T of the frame 150 to ensure that the tips of the concave portions150T of the frame 150 and the bottoms of the concave portions 112Bpressed against each other. As can be seen, in the present embodiment,the stator core 112 is secured on the frame 150 by partialpress-fitting. This press-fitting process forms a fine air gap betweenthe frame 150 and stator core 112. In the present embodiment, when thestator core 112 and stator coil 114 are molded by a molding agent, themolding agent is filled into the air gap formed between the frame 150and stator core 112 at the same time. The engagement section serves as alocking section to prevent the stator core 112 from turning in thecircumferential direction with respect to the frame 150.

As described above, in the present embodiment, the stator core 112 ispartially press-fitted into the frame 150. This arrangement increasesthe sliding property between the frame 150 and stator core 112 andreduces the rigidity. In the present embodiment, this improves theeffect of damping the noise between the frame 150 and stator core 112.In the present embodiment, the air gap between the frame 150 and statorcore 112 is filled with the molding agent, whereby the noise dampingeffect is further improved.

It is also possible to arrange such a configuration that the concaveportions 150T and concave portions 112BO2 are formed in a non-contactstructure and are used only for locking purposes, and the outerperipheral surface of the back core 112B is press-fitted into the innerperipheral surface of the frame 150 other than the concave portions 150Tand concave portions 112BO2.

The stator coil 114 (U1+) and stator coil 114 (U1−), and stator coil 114(U2+) and stator coil 114 (U2−) are positioned symmetrically, relativeto the center of the stator 110. To be more specific, the stator coil114 (U1+) and stator coil 114 (U1−) are located adjacent to each other,and the stator coil 114 (U2+) and stator coil 114 (U2−) are also locatedadjacent to each other. Further, the stator coil 114 (U1+) and statorcoil 114 (U1−), and stator coil 114 (U2+) and stator coil 114 (U2−) arepositioned symmetrically with respect to a line, relative to the centerof the stator 110. To put it another way, the stator coil 114 (U1+) andstator coil 114 (U2+) are placed symmetrically with respect to a line,relative to the broken line C-C passing through the shaft 138. Further,the stator coil 114 (U1−) and stator coil 114 (U2−) are placedsymmetrically with respect to a line.

Similarly, the stator coil 114 (V1+) and stator coil 114 (V1−), andstator coil 114 (V2+) and stator coil 114 (V2−) are positionedsymmetrically with respect to a line. The stator coil 114 (W1+) andstator coil 114 (W1−), and stator coil 114 (W2+) and stator coil 114(W2−) are also positioned symmetrically with respect to a line.

Further, adjacent stator coils 114 of the same phase are continuouslywound in the form of one wire; namely, the stator coil 114 (U1+) andstator coil 114 (U1−) form one wire; namely, the stator coil 114 (U1+)and stator coil 114 (U1−) form one wire, which constitutes two windingcoils. They are each inserted into the tees, and are wound on the tees.Similarly, the stator coil 114 (U2+) and stator coil 114 (U2−) arecontinuously wound in the form of one wire. Similarly, the stator coil114 (V1+) and stator coil 114 (V1−); stator coil 114 (V2+) and statorcoil 114 (V2−); the stator coil 114 (W1+) and stator coil 114 (W1−); andstator coil 114 (W2+) and stator coil 114 (W2−) are continuously woundin the form of one wire, respectively.

Such a symmetric layout with respect to a line and winding of twoadjacent coils of the same phase in the form of one wire provide asimplified connection link structure, when the same or difference phasesare connected by the connection ring, as will be described later withreference to FIG. 4.

The following describes the configuration of the rotor 130. The rotor130 comprises:

a rotor core 132 composed of a magnetic substance;

ten magnets 134 (134A, 134B, 134C, 134D, 134E, 134F, 134G, 134H, 134Iand 134J) bonded on the surface of the rotor core 132 by adhesive; and

a magnet cover 136 arranged on the outer periphery of the magnets 134.The rotor core 132 is secured on the shaft 138.

When the surface (side opposite to the tee 112T of the stator) is anN-pole, the magnets 134 are energized in the radial direction to ensurethat the back side thereof (side bonded to the rotor core 132) will bean S-pole. Further, when the surface (side opposite to the tee 112T ofthe stator) is an S-pole, the magnets 134 are energized in the radialdirection in some cases to ensure that the back side thereof (sidebonded to the rotor core 132) will be an N-pole. The adjacent magnets134 are energized in such a way that the energized poles will alternatewith each other in the circumferential direction. For example, if thesurface of the magnet 134A is attracted by the N-pole, the surfaces ofthe adjacent magnets 134B and 134J are attracted by the S-pole. To putit another way, when the surfaces of the magnets 134A, 134C, 134E, 134Gand 134I are attracted by the N-pole, the magnets 134B, 134D, 134F, 134Hand 134J are attracted by the S-pole.

The magnets 134 have a semicylindrical cross section. Thesemicylindrical shape can be defined as a structure wherein the radialthickness of the right and left in the radial direction is smaller thanthat at the center in the circumferential direction. Such asemicylindrical structure allows the magnetic flux to be distributed inthe form of a sinusoidal wave. Then the induced voltage waveformresulting from the rotation of the EPS motor can be changed into asinusoidal wave, and the amount corresponding to pulsation can bereduced. Reduction in the amount corresponding to pulsation improves thesteering comfort. When a magnet is formed by attraction to the ring-likemagnetic substance, by control of the energizing force, the magneticflux can be distributed in the form similar to the sinusoidal wave, insome cases.

The rotor core 132 is provided with ten large-diameter through-holes132H formed on the concentric circle and five small-diameter recesses132K with protruded inner periphery. The rotor core 132 is composed of alamination of the sheet metal of magnetic substance such as SUS havingbeen stamped out by press molding. The recesses 132K are formed bycrimping the sheet metal at the time of press molding. When a pluralityof sheet metals are laminated, the recesses 132K are fitted with eachother, whereby positioning is performed. The through-hole 132H isintended to cut down the inertia. The rotor balance can be improved bythe through-hole 132H. The outer periphery of the magnet 134 is coveredby the magnet cover 136 to prevent the magnet 134 from being thrownaway. The back core 112B and rotor core 132 can be formed simultaneouslyfrom the same sheet metal by stamping out by a press.

As described above, the rotor 130 of the present embodiment has tenmagnets 134 and ten poles. Also as described above, twelve tees 112T areprovided. The number of slots formed between adjacent tees is 12. To putit another way, the EPS motor of the present invention is a 10-pole12-slot surface magnetic type synchronous motor.

Referring to FIG. 3, the following describes the relationship betweenthe numbers of poles P and slots S in an AC motor.

FIG. 3 is an explanatory diagram representing the relationship betweenthe numbers of poles P and slots S in an AC motor.

In FIG. 3, a combination given by hatching using horizontal linesindicates the relationship between the numbers of poles P and slots Sthat can be used in a three-phase AC motor (brushless motor). Namely,the available combinations include 2 poles and 3 slots, 4 poles and 3slots, 4 poles and 6 slots, 6 poles and 9 slots, 8 poles and 6 slots, 8poles and 9 slots, 8 poles and 12 slots, 10 poles and 9 slots, 10 polesand is 12 slots, and 10 poles and 15 slots. Of these combinations, a10-pole/12-slot combination provided with right and left oblique linesindicates the numbers of motors and slots in the present embodiment. The8-pole/9-slot and 10-pole/9-lot combinations shown by 20 left obliquelines will be described later. The EPS motor shown in FIG. 1 is asmall-sized motor having an outer diameter of 85 mm. Such a small-sizedmotor cannot be achieved if the number of poles N is 12 or more, and istherefore not illustrated.

The motors having 2 poles and 3 slots, 4 poles and 3 slots, 4 poles and6 slots, 6 poles and 9 slots, 8 poles and 6 slots, 8 poles and 12 slots,and 10 poles and 15 slots are provided with similar characteristics. Themotor having 6 poles and 9 slots will be take up as an typical examplein the following explanation:

The 10-pole/12-slot motor of the present embodiment provides a higherusage rate of the magnetic flux of a magnet than the 6-pole/9-slot ACmotor. To be more specific, the 6-pole/9-slot motor has a winding factor(usage rate) (kw) of 0.87 and a skew factor ks of 0.96. The usage rate(kw.ks) of the magnetic flux of the magnet is 0.83. In the meantime, the10-pole/12-slot motor of the present embodiment has a winding factor(usage rate) (kw) of 0.93 and a skew factor ks of 0.99. Thus, it has ausage rate of 0.92. This means that the 10-pole/12-slot motor of thepresent embodiment improves the usage rate of the magnetic flux of amagnet (kw.ks).

The period of the cogging torque corresponds to the least commonmultiple of the numbers of poles P and slots S, and therefore the periodof the cogging torque in the 6-pole/9-slot AC motor is 18. Thus, theperiod of the cogging torque in the 10-pole/12-slot motor of the presentembodiment can be reduced to 60. This shows that a reduction of coggingtorque is ensured.

Further, the cogging torque resulting from poor roundness of innerdiameter can also be reduced. To be more specific, assuming that thecogging torque resulting from the out-of-roundness of inner diameter inthe 6-pole/9-slot AC motor is 3.7, that in the 10-pole/12-slot motor ofthe present embodiment can be 2.4, with the result that the coggingtorque resulting from the out-of-roundness of inner diameter can bereduced. Further, in the present embodiment, machining is applied to theinner diameter of the molded stator subassembly to improve the roundnessof the inner diameter. This leads to further reduction in the coggingtorque resulting from the poor roundness of inner diameter.

Referring to FIG. 4, the following describes the actual measurements ofthe cogging torque in the DC brushless motor for electrical powersteering.

FIG. 4 is an explanatory diagram representing the actual measurements ofthe cogging torque in the DC brushless motor for electrical powersteering of the present embodiment.

FIG. 4(A) shows the cogging torque measured for the angle (mechanical)ranging from 0 through 360°. FIG. 4(B) shows the peak value (mNm) byseparating the high frequency component of the cogging torque shown inFIG. 4(A) for each time order. As described above, time order “60”indicates the period of the cogging torque in a 10-pole/12-slot motorand the cogging torque having occurred is almost zero. Time order “12”is the result of variation in the magnetic field force of the 10-polemagnet. As described above, use of a semicylindrical magnet reduces thecogging torque resulting from variation in magnetic field force down to1.4. The time order “10” is the result of the variation of each tee of a12-slot stator. Since the roundness of the inner diameter by cuttingsubsequent to molding is improved, the cogging torque resulting fromvariation of the tee is also reduced to 2.6.

Time order “0” indicates a DC.component, so-called a loss torque(friction coefficient produced at a speed of zero). The loss torque canalso be lowered to 26.3 mNm. Even when a driver has released thesteering wheel, the loss torque is smaller as compared to the restoringforce of steering wheel to get back to the original position, with theresult that the restoring force of the steering wheel is improved.

As described above, each cogging component can be reduced, the coggingtorque can be reduced to 9 mNm, as shown in FIG. 4(A). The maximumtorque of the EPS motor is 4.5 mNm, and therefore the cogging torque canbe reduce as low as 0.2% (=9 mNm/4.5 Nm) (3/1000 or less of the ratedlevel). The loss torque can also be reduced to 0.57% (=26.3 mNm/4.5 Nm).

The EPS motor 100 of the present embodiment is a motor using an on-boardbattery (e.g. output voltage of 12 volts) as the power source thereof.The EPS motor 100 is mounted close to the steering system or the rack ofa rack/pinion mechanism for transmitting the power of the steeringsystem to the wheel. This requires downsizing due to the limitedinstallation space. In the meantime, a large torque (e.g. 4.5 Nm) isrequired for power assistance of the steering system.

When an attempt is made to deliver the required torque from the AC servomotor powered by a 100 VAC power source, the motor current of about 5amperes is sufficient. However, when 14 VAC obtained by DC-to-ACconversion of the 14 VDC is used for driving, as in the presentembodiment, the motor current must be 70 through 100 amperes in order toget about the same torque with about the same volume. To get such alarge current, the diameter of stator coil 114 must be increased to aslarge as 1.6 mm. In this case, the number of turns of the stator coil114 is 14 (T). The number of turns of the stator coil 114 is in therange from 9 through 21, although it depends on the diameter of thestator coil 114. When the diameter of the stator coil 114 is 1.8 mm, thenumber of turns is 9. Here if the coil having a diameter of 1.6 mminstead of the coil having a diameter of 1.8 is used for winding, coilspace factor can be improved by 75%, for example. Since the coil spacefactor can be improved, the current density can be reduced in relativeterms. This arrangement reduces the copper loss and keeps down motortemperature rise. Further, it improves the rpm/torque characteristics.Some of the recent powered vehicles are equipped with a 42-volt battery.In this case, this arrangement reduces the motor current. The number ofturns of the stator coil 114 is in the range from 20 through 30.

In the adjacent tees 112T, the space W1 (e.g. tee 112T (U1−) of theexpanded section of the tip (side facing the rotor 130) of the tee 112Tand the space W1 (circumferential space at the position closest to thecircumferential direction) of the expanded section of the tip tee 112T(W1−) are 1 mm. Reducing the tee space in this manner decreases thecogging torque. Even if vibration is applied to the motor, the line ofthe stator coil 114 is larger than the space W1, and this preventsstator coil 114 from being dropped out on the rotor side. Theappropriate space W1 between adjacent tees is 0.5 through 1.5 mm, forexample, which is smaller than the diameter of the stator coil 114. Asdescribed above, in the present embodiment, the space W1 of the adjacenttees is smaller than the diameter of the stator coil 114.

Referring to FIGS. 5 and 6, the following describes the connection ofstator coils in a DC brushless motor for electrical power steering inthe present embodiment:

FIG. 5 is a connection diagram of stator coils in the DC brushless motorfor electrical power steering according to the present embodiment. FIG.6 is a side view representing the electrical connection of the statorcoils in the DC brushless motor for electrical power steering accordingto the present embodiment of the present embodiment. FIG. 6 is a view inthe direction of the arrow B-B in FIG. 1. The same reference numerals asthose in FIG. 2 indicate the same parts.

In FIG. 5, coil U1+ denotes a stator coil 112T (U1+) shown in FIG. 2.Coils U1−, U2+, U2−, V1+, V1−, V2+, V2−, W1+, W1−, W2+, W2− indicate thestator coils 112T (U1−) . . . 112T (W2−) of FIG. 2.

In the stator coil of the present embodiment, a delta connection is usedfor U, V and W phases. Each phase constitutes a parallel circuit. To bemore specific about the U phase, a parallel connection of coil U2+ andcoil U2− is provided for the series connection of coil U1+ and coil U1−.Here as described above, the coil U1+ and coil U1− are formed bycontinuous winding of a wire. This is also applicable to the V and Wphases.

A star-connection method can also be used for this connection. The deltaconnection allows the lower terminal voltage than the star connection.For example, assuming that the voltage across the series/parallelcircuit of the U phase is E. The terminal voltage is E, but this is√{square root over (3)} E in the star connection. Since the terminalvoltage can be reduced, the number of turns of the coil can be increasedand a small-diameter wire can be utilized. Further, as compared to thecase of four coils in series, a parallel circuit reduces the currentflowing to each coil, and this allows use of a smaller-diameter wire andimproves the coil space factor, with the result that better bendingproperties and easier in production are ensured.

Referring to FIGS. 5 and 6, the following describes the connectionmethod for three phases and each phase, using a connection ring.

As shown in FIG. 5, coils U1−, U2−, V1+ and V2+ are connected by theconnection ring CR (UV); coils V1−, V2+, W1+ and W2+ are connected bythe connection ring CR (VW); and coils U1+, U2+, W1− and W2− areconnected by the connection ring CR (UW). Through these connections, athree-phase delta connection is made.

As shown in FIG. 6, three connection rings CR (UV), CR (VW) and CR (UW)are used. The connection rings CR (UV), CR (VW) and CR (UW) are formedby bending and machining the bus bar type connection board bent in acircular arc so as to feed a large current. Each of the connection ringshas the same shape. For example, the connection ring CR (UV) is formedby a connection between a circular arc of a small radius and a circulararc of a large radium. Other connection rings CR (VW) and CR (UW) aremade in the same structure. These connection rings CR (UV), CR (VW) andCR (UW) are retained by the holders H1, H2 and H3 in the state displaced120° in the circumferential direction. The connection ring CR andholders H1, H2 and H3 are molded together with the coil end using amolding agent.

In the meantime, in FIG. 6 the stator coil terminal T (U1+) is oneterminal of the stator coil 114 (U1+) wound with the stator coil 112T(U1+). The stator coil terminal T (U1+) is one terminal of the statorcoil 114 (U1−) wound with the stator coil 112T (U1−) As described above,the stator coil 114 (U1+) and stator coil 114 (U1−) are form acontinuous coil in the form of one wire. Two terminals T (U1+) and T(U1−) are present for two coils, stator coil 114 (U1+) and stator coil114 (U1−). The stator coil terminals T (U2+), T (U2−), T (V1+), T (V1−),T(V2+), T(V2−), T (W1+), T (W1−), T (W2+) are T (W2−) are the terminalson one side of the stator coil 114 (U2+), . . . (W2+).

The stator coil terminals T (U1−), (U2−), (V1+) and (V2+) are connectedby the connection ring CR (UV), whereby the coils U1−, U2−, V1+ and V2+shown in FIG. 5 are connected by the connection ring CR (UV). The statorcoil terminal T (V1−), T (V2−), T (W1+) and T (W2+) are connected by theconnection ring CR (VW), whereby the coils V1−, V2−, W1+ and W2+ shownin FIG. 5 are connected by the connection ring CR (UW).

Referring to FIG. 7, the following describes another example of theconfiguration of the stator 110. FIG. 7 is a view in the direction ofthe arrow A-A in FIG. 1. The same reference numerals as those in FIG. 2indicate the same parts.

In the stator 110 shown in FIG. 2, the stator core 112 is composed of anannular back core 112B and a plurality of tees 112T provided separatelyfrom this annular back core 112B. By contrast, in the present example,it is composed of twelve T-shaped tee-integrated split back cores; 112(U1+), 112 (U1−) 112 (U2+), 112 (U2−), 112 (V1+), 112 (V1−), 112 (V2+),112 (V2−), 112 (W1+), 112 (W1−) and 112 (W2+), 112 (W2−). To be morespecific, the annular back core 112B of FIG. 2 is split into twelvepieces in the circumferential direction. A tee is integrated with eachof the split back core piece. The tee-integrated split back cores 112(U1+) . . . 112 (W2−) are composed of a lamination of the sheet metal ofmagnetic substance such as a silicon steel plate having been stamped outby press molding. The rotor 130 is formed as shown in FIG. 2.

Stator coils 114 (U1+), 114 (U1−), 114 (U2+) 114 (U2−), 114 (V1+), 114(V1−), 114 (V2+), 114 (V2−), 114 (W1+), 114 (W1−), 114 (W2+) and 114(W2−) are wound on the tees of the tee-integrated split back cores 112(U1+) . . . 112 (W2−), namely, on twelve independent tees 112T (U1+) . .. 112T (W2−), in a concentrated winding. The stator coil 114 (U1+) . . .114 (W2−) is wound in the direction shown in FIG. 2.

The stator coils 114 (U1+) . . . 114 (W2−) are wound on thetee-integrated split back cores 112 (U1+) . . . 112 (W2−), respectively.Then the fitting type convex portions are press-fitted into the concaveportions formed on the end faces of the tee-integrated split back cores112 (U1+) . . . 112 (W2−) in the circumferential direction, wherebyassembling of the stator 110 terminates. A plurality of positions on theouter periphery of the back core 112B are press-fitted with the innerperiphery of the frame 150. Under this condition, the stator core 112and stator coil 114 are integrally molded by thermosetting resin MR toform a stator subassembly. In the present embodiment has referred to thecase where the stator coil 114 built in the stator core 112 ispress-fitted with the frame 150. Under this condition, the stator core112 and stator coil 114 are integrally molded. This procedure has beendescribed so far. It is also possible to make such arrangements that,with the stator coil 114 is built in the stator core 112, the statorcore 112 and stator coil 114 are integrally molded and the stator core112 is press-fitted with the frame 150 subsequently.

In the processing of molding with molding agent, the jig (notillustrated) is mounted on the structure composed of the stator core 112and frame 150 in such a way that the stator core 112 and the coil end ofthe stator coil 114 protruding axially from the axial end of the statorcore 112 will be enclosed by the jig (not illustrated) and frame 150.Liquid molding agent is poured into the space enclosed by the jig (notillustrated) and the frame 150, thereby filling the molding agent intothe air gap between the core end and stator core 112, the air gap of thestator coil 114, the air gap between stator core 114 and stator coil114, and the air gap between the stator core 112 and frame 150. Then themolding agent is solidified. After it has solidified, the jig (notillustrated) is removed.

The inner peripheral surfaces of the molded stator subassembly, namely,the tips of the tees of the tee-integrated split back cores 112 (U1+) .. . 112 (W2−) as the surfaces radially opposite to the rotor 130 areprovided with machining. This arrangement reduces the variation of theair gap between the stator 110 and rotor 130, and further improves theroundness in the inner diameter of the stator 110. Further, integralmolding ensure effective release of the heat generated by electricconduction of the stator coil 114, as compared to the case whereintegral molding is not adopted. Further, the molding process protectsthe stator coil and tee against vibration. Further, machining of theinner diameter subsequent to molding reduces the cogging torqueresulting from the roundness of the inner diameter. Reduction of thecogging torque improves the steering comfort of the steering system.

Concave portions 150T are arranged inside the frame 150. Concaveportions 112BO2 are arranged on the outer periphery of the back core112B so as to be engaged with the concave portions 150T. The concaveportions 150T and concave portions 112BO2 constitute an engagementsection IP having a mutually different curvature rate for engagementwith each other. They are continuously formed in the axial direction.Eight of these portions are arranged at a predetermined interval in thecircumferential direction. The engagement section also serves as apress-fit section. To be more specific, when the stator core 112 issecured on the frame 150, the concave portions 112BO2 of the back core112B are press-fitted into the concave portions 150T of the frame 150 toensure that the tips of the concave portions 150T of the frame 150 andthe bottoms of the concave portions 112B pressed against each other. Ascan be seen, in the present embodiment, the stator core 112 is securedon the frame 150 by partial press-fitting. This press-fitting processforms a fine air gap between the frame 150 and stator core 112. In thepresent embodiment, when the stator core 112 and stator coil 114 aremolded by a molding agent, the molding agent is filled into the air gapformed between the frame 150 and stator core 112 at the same time. Theengagement section serves as a locking section to prevent the statorcore 112 from turning in the circumferential direction with respect tothe frame 150.

As described above, in the present embodiment, the stator core 112 ispartially press-fitted into the frame 150. This arrangement increasesthe sliding property between the frame 150 and stator core 112 andreduces the rigidity. In the present embodiment, this improves theeffect of damping the noise between the frame 150 and stator core 112.In the present embodiment, the air gap between the frame 150 and statorcore 112 is filled with the molding agent, whereby the noise dampingeffect is further improved.

It is also possible to arrange such a configuration that the concaveportions 150T and concave portions 112BO2 are formed in a non-contactstructure and are used only for locking purposes, and the outerperipheral surface of the back core 112B is press-fitted into the innerperipheral surface of the frame 150 other than the concave portions 150Tand concave portions 112BO2.

Referring to FIG. 8, the following describes the configuration of asteering system using the DC brushless motor for electrical powersteering of the present invention.

FIG. 8 is a system configuration diagram representing the configurationof a steering system using the DC brushless motor for electrical powersteering of the present embodiment.

When the steering ST is turned, the rotation drive force is deceleratedby a manual steering gear STG through the rod RO and is transmitted toright and left tie rods TR1 and T2 to steer the right and left wheel WH1and WH2.

The EPS motor 100 of the present embodiment is mounted close to themanual steering gear STG. The drive force is transmitted to the manualsteering gear STG through a gear GE. The rod RO is equipped with atorque sensor TS, which detects the rotation drive force (torque)applied to the steering ST. Based on the torque sensor TS, thecontroller 200 controls the current supplied to the motor in such a waythat the output torque of the EPS motor 100 will be the target torque.The controller 200 and EPS motor 100 is supplied with power from abattery BA.

The aforementioned configuration indicates a rack type power steeringsystem with the EPS motor mounted close to the rack/pinion mechanism.The EPS motor 100 of the present invention is also applicable to acolumn type power steering system with the EPS motor mounted close tothe steering system.

Referring to FIG. 9, the following describes the configuration of acontroller for controlling the DC brushless motor for electrical powersteering of the present embodiment.

FIG. 9 is a function block diagram representing the configuration of thecontroller for controlling the DC brushless motor for electrical powersteering of the present invention.

The controller 200 comprises a power module 210 having a function as aninverter; and a control module 220 for controlling the power module 210.The DC voltage from the battery BA is converted to the 3-phase ACvoltage by the power module 210 having a function as an inverter, and issupplied to the stator coil 114 of the EPS motor 100.

The torque control 221 in the control module 220 calculates the torqueTe based on the torque Tf of the steering ST detected by the torquesensor TS and the target torque Ts, and outputs the torque command, i.e.current command Is and rotary angle θ1 of the rotor 130 thereto by thePI control (P: proportional item; I: integration item).

The phase shift circuit 222 outputs the pulse from the encoder E, i.e.the position information θ of the rotor by shifting the phase thereof,in response to the command of the rotary angle θ1 from the torquecontrol circuit (ASR) 221. Based on the position information θ of theresolver 156 for detecting the position of the pole of permanent magnetand the rotor with its phase shifted by the phase shift circuit 222, asine/cosine wave generator 2223 outputs the sinusoidal wave obtained byshifting the phase of the induction voltage of each of the windings(three-phase in this case) of the stator coil.

The 2-phase/3-phase conversion circuit 224 outputs the current commandsIsa, Isb and Isc to respective phases in response to the current commandIs from the torque control circuit (ASR) 221 and the output from thesine/cosine wave generator 223. These phases are separately providedwith current control systems 225A, 225B and 225C, respectively. The2-phase/3-phase conversion circuit 224 sends the signals conforming tothe current commands Isa, Isb and Isc, and current detection signalsIfa, Ifb and Ifc from the current detector CT, to the inverter 210 tocontrol the currents of these phases.

The aforementioned description refers to the 10-pole/12-slot EPS motor.The following describes the 8-pole/9-slot EPS motor and 10-pole/9-slotEPS motor with reference to the hatched area in FIG. 3.

The 8-pole/9-slot and 10-pole/9-slot motors provide a higher usage rateof the magnetic flux of a magnet than the 6-pole/9-slot AC motor. To bemore specific, the 6-pole/9-slot AC motor has a usage rate of themagnetic flux of a magnet (kw.ks) of 0.83. In the meantime, the8-pole/9-slot and 10-pole/9-slot motors have a winding factor (kw) of0.95 with a skew factor (ks) of 1.00. Thus, the 8-pole/9-slot and10-pole/9-slot motors have a usage rate (kw.ks) of 0.94. This means thatthe 8-pole/9-slot motor and 10-pole/9-slot motors improve the usage rateof the magnetic flux of a magnet (kw.ks).

The period of the cogging torque corresponds to the least commonmultiple of the numbers of poles P and slots S, and therefore the periodof the cogging torque in the 6-pole/9-slot AC motor is 18. Thus, theperiod of the cogging torque in the 8-pole/9-slot and 10-pole/9-slotmotors can be reduced to 72. This shows that a reduction of coggingtorque is ensured.

Further, the cogging torque resulting from poor roundness of innerdiameter can also be reduced. To be more specific, assuming that thecogging torque resulting from the out-of-roundness of inner diameter inthe 6-pole/9-slot AC motor is 3.7, that in the 8-pole/9-slot and10-pole/9-slot motors can be 1.4, with the result that the coggingtorque resulting from the out-of-roundness of inner diameter can bereduced. Further, machining is applied to the inner diameter of themolded stator subassembly to improve the roundness of the innerdiameter. This leads to further reduction in the cogging torqueresulting from the poor roundness of inner diameter.

In the 8-pole/9-slot and 10-pole/9-slot motors, parallel connection ofthe series circuit of the coil U2+ and coil U2− cannot be configured asviewed from the U phase, with respect to the series circuit of the coilU1+ and coil U1−, as in the 10-pole/12-slot EPS motor described abovewith reference to FIG. 5. This requires a series connection of the coilU1+, coil U1−, coil U2+ and coil U2−.

Referring to FIGS. 10 through 16, the following describes the controllerof the DC brushless motor for electrical power steering of the presentembodiment.

FIG. 10 is a perspective exploded view representing the configuration ofthe controller of the DC brushless motor for electrical power steeringof the present embodiment.

As shown in FIG. 10, the motor controller 200 comprises a power module210, a control module 220, a conductor module 230, a case 240 and ashield cover 250.

In the power module 210, a wiring pattern is formed on a metallicsubstrate through an insulator. A semiconductor switching device SSWsuch as a MOSFET (metal oxide semiconductor field-effect transistor)described with reference to FIG. 9 is mounted on the wiring pattern. Thepower module 210 is fixed with one end of each of multiple lead frames210 LF by soldering. The lead frames 210 LF is used for electricalconnection of the power module 210 and control module 220.

In the control module 220, a CPU and driver circuit are mounted on thePCB substrate. In the illustrated state, the CPU and driver circuit aremounted on the lower surface of the substrate. The signal connector 220Cis mounted on the control module 220.

The conductor module 230 is integrally connected with the bus bar 230Bas a power line by molding. At the same time, it is connected integrallywith the motor connector 230 SC as a terminal for supplying motorcurrent to the motor and the power connector 230 PC by molding. Theparts 230P such as a relay coil and a capacitor are mounted in advanceon the conductor module 230. The terminal of the parts 230P and bus bar230B are secured by TIG welding (arc welding).

The case 240 is made of aluminum. At the time of assembling, the powermodule 210 and conductor module 230 are fixed by screws in the case 240.The control module 220 is also fixed by screws on the power module 210and conductor module 230. The multiple ends of the lead frames 210 LF isconnected with the terminal of the control module 220 by soldering. Theshield cover 250 is fixed by screws in the final step, whereby the motorcontroller 200 is manufactured.

FIG. 11 is a circuit diagram representing the circuit configuration ofthe controller for controlling the DC brushless motor for electricalpower steering of the present embodiment. The same reference numerals asthose in FIG. 10 indicate the same parts.

The motor controller 200 comprises a power module 210, control module220 and conductor module 230.

The conductor module 230 is integrally molded with the bus bar 230B. Inthe drawing, the bold solid line indicates the bus bar. In the conductormodule 230, the common filter CF, normal filter NF, capacitors CC1 andCC2, and relay RY1 are connected to the bus bar for connecting thecollector terminal of the semiconductor switching device SSW, as shownin the drawing.

The portion indicated by a double circle denotes the welded connection.For example, the four terminals of the common filter CF are connected tothe bus bar terminal by welding. Two terminals of the normal filter, twoterminals of each of ceramic capacitors CC1 and CC2 and two terminals ofthe relay RY1 are also connected to the terminals of the bus bar bywelding. The common filter CF and normal filter NF are provided to avoidradio noise.

A bus bar is also used for the wire for supplying motor current to themotor 100 from the power module 210. Relays RY2 and RY3 are connected bywelding to the bus bar wire leading from the power module 210 to themotor 100. Relays RY1, RY2 and RY3 are used for the fail safe system tocut off power to the motor in the event of motor failure or controlmodule trouble.

The control module 220 is provided with a CPU 222 and driver circuit224. Based on the torque detected by the torque sensor TS and the rotaryposition of the motor 100 detected by the resolver 156, the CPU 222outputs to the driver circuit 224 the control signal for controllingon-off operation of the semiconductor switching device SSW of the powermodule 210. Based on the control signal from the CPU 222, the drivercircuit 224 controls the on-off drive of the semiconductor switchingdevice SSW of the power module 210. The motor current supplied from thepower module 210 to the motor is detected by the motor current detectionresistors (shunt resistors) DR1 and DR2 and is amplified by theamplifiers AP1 and AP2. Then the current is inputted into the CPU 222.The CPU 222 provides feedback control to ensure that the motor currentwill be the target. The CPU 222 is connected by the external enginecontrol ECU, CAN and others, whereby information is exchanged.

The A (inverted delta symbol) in the drawing indicates the portionsconnected by welding using the lead frame. Use of the lead frame reducesthe stress. The configuration of the lead frame will be described withreference to FIG. 15. Welding using the lead frame is utilized forelectrical connection between the control module 220 and power module210 or conductor module 230.

The power module 210 comprises six semiconductor switching devices SSWsuch as IGBT. The semiconductor switching device SSW is seriallyconnected to the upper and lower arms for each of three phases. In thedrawing, a cross “x” denotes an electrical connection by wire bonding.To be more specific, motor current is supplied to the motor 100 from thepower module 210 through the bus bar of the conductor module 230, butthis is a large current. Accordingly, connection is made by wire bondingthat allows a large current to run, and reduces the stress. The detailswill be described later with reference to FIG. 16. The power supply lineand earth line for the semiconductor switching device SSW are alsoconnected wire bonding.

Referring to FIG. 12, the following describes the configuration of theconductor module 230 of the controller for controlling the DC brushlessmotor for electrical power steering of the present embodiment.

FIG. 12 is a perspective bottom view showing the configuration ofconductor module of the controller for controlling the DC brushlessmotor for electrical power steering. The same reference numerals inFIGS. 10 and 11 indicate the same parts. FIG. 12 shows the bottom viewof the conductor module 230 shown in FIG. 10.

The conductor module 230 is formed by molding, and is provided withholes for inserting the terminals of electrical parts such as the commonfilter CF, normal filter NF, capacitors CC1 and CC2, and relays RY1, RY2and RY3. Electrical parts are arranged on these positions, and theterminals of the electrical parts and terminals of the bus bar areconnected by welding on the illustrated bottom surface side.

FIG. 13 is a perspective view representing the configuration of thecontroller for controlling the DC brushless motor for electrical powersteering of the present embodiment.

In FIG. 13, the power module 210 and conductor module 230 are arrangedin the case 240. The control module 220 is not yet mounted in position.

The conductor module 230 and a plurality of bus bars BB1, BB2, BB3, BB4,BB5, BB6 and BB7 are formed by molding. The bus bar terminals andterminals of the electrical parts such as the common filter CF, normalfilter NF, capacitors CC1 and CC2, and relays RY1, RY2 and RY3 areconnected by welding.

The power module 210 is provided with a plurality of semiconductorswitching device SSW. Electrical connections are provided by wirebonding WB1, WB2, WB3, WB4 and WB5 at five positions between the powermodule 210 and conductor module 230. For wire bonding WB1, for example,five aluminum wires having a diameter of 500 μm are connected inparallel.

The power module 210 and conductor module 230 are arranged opposite toeach other on one and the same flat plane. To be more specific, thepower module 210 is mounted on one side of the case 240, and theconductor module 230 is located on the other side of the case 240. Thisarrangement ensures easier wire bonding work.

FIG. 14 is a cross sectional view of the controller for controlling theDC brushless motor for electrical power steering of the presentembodiment. It shows the cross sectional configuration at position X1-X1of FIG. 13. The same reference numerals in FIGS. 10 through 13 indicatethe same parts.

The power module 210 and conductor module 230 are fixed by screws on theinner bottom surface of the case 240. As shown in FIG. 11, the conductormodule 230 are provided with electrical parts and is welded togetherwith the bus bar, thereby forming an integral module, which is fixed byscrews. Then electrical connection between the power module 210 andconductor module 230 is provided by wire bonding WB.

The lower end of the lead frames LF is secured on the power module 210by soldering. Under this condition, the control module 220 is placedthereon and is secured the other end of the lead frames LF by soldering.The control module 220 is secured on the case 240 by screws. A shieldcover 250 is then fixed on the case 240 by screws.

FIG. 15 is a cross sectional view representing the major portions of thecontroller for controlling the DC brushless motor for electrical powersteering of the present embodiment. The same reference numerals as thosein FIG. 14 indicate the same parts.

FIG. 15 indicates a detailed structure of the connections between thepower module 210 and conductor module 230.

The power module 210 is provided with a semiconductor switching deviceSSW. A metal substrate MP (e.g. aluminum (Al) and copper (Cu)) is usedto release the heat thereof. Heat conduction grease HCG is appliedbetween the metal substrate MP and case 240. Thus, the heat generatedfrom the semiconductor switching device SSW is released from thealuminum case 240 through therebetween heat conduction grease HCG. Awiring pattern WP is formed on the metal substrate MP through theinsulation film 1M. An insulation layer of low elasticity is used toproduce the insulation film 1M. The wiring pattern WP is obtained byetching and patterning a 175 μm-thick copper (Cu) foil. An aluminum padPD used for electrical connection is formed on the wiring pattern WP. Anickel film is formed on the back of the aluminum pad PD.

For the conductor module 230, in the meantime, a bus bar BB is formed.On the end of the bus bar BB, a nickel film is formed on the surface ofthe connection with the power module 210.

Wire bonding WB is used for connection between the bus bar BB of thepower module 210 and the aluminum pad PD of the conductor module 230 bymeans of an aluminum wire.

As described above, the metallic substrate is used as a conductor module230. This arrangement causes expansion coefficient to be increased.Since expansion and compression are repeated in conformity to thetemperature change of the conductor module 230, stress is applied to theelectrical connection with the power module 210. Because a large currentruns between the power module 210 and conductor module 230, such aconductor as a bus bar is preferably utilized for connection. However,this may cause separation of the connection due to thermal stress. Tosolve this problem, an aluminum wire susceptible to reversible change isused, as in the present embodiment. This allows thermal deformation ofthe conductor module 230 to be absorbed by the aluminum wire, with theresult that stress is not applied to the electrical connection. Thisprovides a stress-free structure. However, to allow a large current toflow, five aluminum wires having a diameter of 500 μm are connected inparallel.

A wire pattern is obtained by etching and patterning a 175 μm-thickcopper (Cu) foil. If the thickness is in the range from 105 through 200μm, for example, resistance can be reduced, and the amount of heatgeneration can also be reduced in the face of a large current. It ismore preferably to use a wire pattern having a thickness of 145 through175 μm. Use of a wire pattern having a thickness of 145 μm or moreallows the resistance to be reduced as compared to the thickness of 105μm. The amount of heat generation can also be reduced in the face of alarge current. Further, when a copper foil having a thickness of 200 μmis patterned by etching, the pattern pitch will be increased and a smallchip resistor or chip capacitor may not be installed in some cases. Ifthe thickness is 175 μm or more, smaller chip parts can be utilized.

FIG. 16 is a cross sectional view representing the major portions of thecontroller for controlling the DC brushless motor for electrical powersteering of the present embodiment. The same reference numerals as thosein FIG. 14 indicate the same parts.

The power module 210 and control module 220 are connected by the leadframes LF. The lead frames LF used in the present embodiment is made ofa brass sheet material having a thickness of 0.15 mm, for example, andhas a bend at some midpoint as shown in the drawing. As described above,the metal substrate MP is used as the substrate of the power module 210.Accordingly, the aforementioned lead frames LF is used to preventthermal stress from being applied to the electrical connection betweenthe power module 210 and control module 220 by thermal stress. Solderingis used for connection between the power module 210 and one end of thelead frames LF, and between the control module 220 and the other end ofthe lead frames LF. This arrangement provides signal line connectionwith a stress-free structure.

Referring to FIG. 17, the following describes another configuration ofthe controller for controlling the DC brushless motor for electricalpower steering of the present embodiment.

FIG. 17 is a perspective view representing another configuration of thecontroller for controlling the DC brushless motor for electrical powersteering of the present embodiment. The same reference numerals in FIGS.10 through 16 indicate the same parts.

Basically, the structure of the present embodiment is the same as shownin FIGS. 10 and 12, and the circuit configuration is the same as shownin FIG. 11. FIG. 17 shows the power module 210 and conductor module 230Amounted in the case 240, where the control module 220 is not yetmounted.

In this example, the configuration of the conductor module 230A isslightly different from that of the conductor module 230 illustrated inFIG. 13. To be more specific, the conductor module 230A is L-shaped inits planer geometry, as compared with the conductor module 230 shown inFIG. 13 being rectangular. The terminals of the electrolytic capacitorand ceramic capacitor are fixed to the bus bar by welding at the portionY1. At another portion Y2, the terminals of the relay, normal filter andcommon filer are secured to the bus bar by TIG welding (arc welding), asin FIG. 13.

As described above, according to the present embodiment, welding is usedfor connection between the power module 210 and conductor module 230.Connection between the control module 220 and power module 210 isprovided by soldering. According to this method, the portion exposed toa large current is connected by welding, whereby melting of weldingconnection is avoided and the reliability is improved. Other positionsare connected by soldering, thereby improving the manufacturability.

Connection between the power module 210 and conductor module 230 isprovided by wire bonding. This arrangement reduces the stress on a largecurrent line. Further, parallel connection of a plurality of wiresallows a large current to run.

The power module 210 and conductor module 230 are arranged on the sameplane opposed to each other. To be more specific, the power module 210and conductor module 230 are arranged on one side of the case 240. Theconductor module 230 is placed on the other side of the case 240. Thisarrangement ensures easier wire bonding work.

1. A DC brushless motor for electrical power steering for outputting thesteering torque, controlled by a power conversion apparatus forconverting the power obtained from an on-board power source, intopolyphase a.c. power and for outputting the power, said DC brushlessmotor for electrical power steering comprising: a frame; a statorsecured on said frame; a rotor arranged opposite to said stator throughan air gap; a flange for blocking both ends of the frame in the axialdirection; and a sensor for checking the magnetic pole position of therotor said stator comprising; a stator core; and a polyphase stator coilbuilt in said stator core; said stator core, formed by connecting aplurality of split core pieces, comprising: an annular back core; and aplurality of tee cores projected radially from said back core; wherein aslot is formed on said tee core adjacent to said stator core, and saidstator coil is composed of a plurality of unit coils, and isincorporated in said slot; said rotor comprising: a shaft; a rotor coreprovided on the shaft; and a plurality of magnets fixed onto the surfaceof the outer periphery of the rotor core; said DC brushless motor forelectrical power steering further characterized in that said stator coreand stator coil are molded by a molding agent, with the stator coilincorporated in the stator core, said shaft being rotatably supported bya bearing, said bearing being arranged on the flange, one side of saidflange being provided with a recess, said recess, as a cylindricalmember concentric with the shaft, being located inward of the axial endof the frame and extending to the position opposed to the coil end, andone side of said bearing being arranged on the position of the recessradially opposite to the coil end.
 2. The DC brushless motor forelectrical power steering described in claim 1, wherein the sensor isarranged on the axial end of the frame, and the flange with the recessarranged thereon blocks one of the axial ends of the frame, equippedwith the sensor.
 3. The DC brushless motor for electrical power steeringdescribed in claim 2, wherein one end of said shaft in the axialdirection expends further in the axial direction than one side of thebearing and reaches said recess, and said sensor is arranged in the airgap between the outer peripheral surface of the shaft and the peripheralsurface of the recess.
 4. The DC brushless motor for electrical powersteering described in claim 3, said sensor comprising: a census testerwith a coil wound on the core; and a sensor rotor arranged opposite tothe census tester; wherein said census tester is secured on theperipheral surface of the recess, while the sensor rotor is secured onthe outer peripheral surface of the shaft so as to be positionedopposite to the census sensor through the air gap.
 5. The DC brushlessmotor for electrical power steering described in claim 1, wherein aplurality of unit coils are electrically connected for each phase by theconnection member arranged on one side of the coil end, and the flangeequipped with said recess blocks the end on the side axially opposite tothe coil end equipped with said connection member.
 6. The DC brushlessmotor for electrical power steering described in claim 1, wherein theother end of the flange has a recess on the side axially opposite to thecoil end, said recess on the other end of the flange being engaged withthe tip of the coil end.
 7. The DC brushless motor for electrical powersteering described in claim 1, wherein the coil end opposite axially tothe other end of the flange is covered with said molding agent so thatan air gap is formed between the frame and air space; the other end ofsaid flange provided with an annular protrusion extending in the axialdirection, and said protrusion being engaged with the air gap when theother end of the flange is secured on the frame.
 8. A DC brushless motorfor electrical power steering manufacturing method, driven by polyphasealternating current power, for outputting steering torque, saidmanufacturing method comprising: a first step of assembling a statorcoil into a stator core; a subsequent second step of press-fitting intothe frame a plurality of positions of the stator core incorporating thestator coil in the circumferential direction, and obtaining a structurecomposed of the stator core incorporating the stator coil, secured tothe frame; a subsequent third step of mounting a jig on said structurein such a way that the jig and frame will enclose the stator core andthe coil end of the stator coil protruding axially from the axial end ofthe stator core; a subsequent fourth step of injecting the molding agentinto the space enclosed by the jig and frame, thereby filling themolding agent into the air gap between the coil end and stator core, theair gap of the stator coil, the air gap between stator core and statorcoil, and the air gap between the stator core and frame; a subsequentfifth step of solidifying the molding agent; and a subsequent sixth stepof removing the jig.
 9. The DC brushless motor for electrical powersteering manufacturing method described in claim 8, further comprisingthe steps of preparing a plurality of serrated coil pieces with coil bywinding a coil on the serrated core piece; and connecting a plurality ofserrated coil pieces with coil, to annular core pieces, therebyobtaining said stator core incorporating the stator coil.
 10. The DCbrushless motor for electrical power steering manufacturing methoddescribed in claim 8, further comprising the steps of: preparing aplurality of T-shaped core pieces with coil, by winding the coil on theprotruded portion of the T-shaped core piece; and connecting a pluralityof T-shaped core pieces in the circumferential direction, therebyobtaining said stator core incorporating the stator coil.
 11. The DCbrushless motor for electrical power steering manufacturing methoddescribed in claim 8, further comprising the steps of: electricallyconnecting one side of the coil end to a plurality of unit coilsconstituting the stator coil using a connection member; electricallyconnecting said connection member to a cable extending outside from theframe; and molding one side of the coil end with said molding agent insuch a way that the connection member and part of the cable are moldedtogether with one side of the coil end by the molding agent.